Linear particle accellerators

ABSTRACT

Linear particle accelerator of compact dimensions, intended for industrial or medical applications, comprising, in a vacuum enclosure, a particle source and an accelerating structure having an input coupler connected to a waveguide extending along the lateral and end walls of said accelerating structure, the waveguide portion located against the end wall of said structure being provided with two holes located along the beam path for the passage of accelerated particles; a hood arrangement groups all parts of the accelerating device (accelerator, UHF electromagnetic power source, voltage supplies).

United States atent [191 Henry-Bezy et al.

[ Mar. 12, 1974 LINEAR PARTICLE ACCELERATORS [75] Inventors: GeorgesHenry-Bezy; Hubert P. Leboutet, both of Paris, France [73] Assignee:Thomson-CSF, Paris, France [22] Filed: Apr. 25, 1972 [21] Appl. N0.:247,346

[30] Foreign Application Priority Data 2,899,598 8/1959 Ginzton 3l5/5.42X

3,292,239 12/1966 Sadler 315/539 X 3,171,054 2/1965 Dong et al. 3l5/3.5

Primary Examiner-Eli Lieberman Assistant Examiner-Saxfield Chatmon, Jr.

Attorney, Agent, or Firm-Cushman, Darby & Cushman [57] ABSTRACT Linearparticle accelerator of compact dimensions, intended for industrial ormedical applications, comprising, in a vacuum enclosure, a particlesource and an accelerating structure having an input coupler connectedto a waveguide extending along the lateral and end walls of saidaccelerating structure, the waveguide portion located against the endwall of said structure being provided with two holes located along thebeam path for the passage of accelerated particles; a hood arrangementgroups all parts of the accelerating device (accelerator, UHFelectromagnetic power source, voltage supplies).

7 Claims, 8 Drawing Figures MODULATOR PATENTED MAR i 2 I974 SHtEI l U? 4PATENTED MAR I 2 1974 SHEET 3 0F 4 PATENTED MAR I 2 1914 sum u 0F 4 llLINEAR PARTICLE ACCELERATORS The present invention relates to linearparticle accelerators, in particular electron accelerators, and relatesmore particularly to accelerators of compact design.

Compact linear accelerators of this kind are generally intended formedical applications such as gamma radiography or radiotherapy, in whichthe high-energy particles bombard a target made of a metal having a highatomic number which metal emits X-rays or gamma-rays under the influenceof said bombardment. The compact design of the accelerator is even moreimportant where the equipment has to be spatially mobile, that is to sayto be capable of being aligned in order that the radiation emitted bythe target can be directed to the desired location (organ beingirradiated).

The known accelerators of this type generally have a relativelysubstantial bulk and are therefore difficult to manipulate.

The acclerator in accordance with the invention enables these drawbacksto be overcome. In this accelerator, in other words, the essentialelements are arranged along the accelerator section and rotated inside acylinder of reduced dimensions.

In accordance with the invention,a linear particle accelerator comprisesa vacuum enclosure in which is located a source producing a particlebeam, an accelerating structure and means to inject hyperfrequencyenergy in said structure, said means comprising at least a foldedwaveguide entirely located within said enclosure, along saidaccelerating structure said structure being formed with a succession ofcylindrical elements provided with notches said waveguide being locatedwithin said notches.

For a better understanding of the invention and to I show how the samemay be carried into effect, reference will be made to the drawings,given solely by way of example, which accompanies the followingdescription and wherein FIG. 1 illustrates a longitudinal section of anaccelerator in accordance with the invention.

FIGS. 2, 3 and 4 illustrate a partial transversal section of anaccelerator in accordance with the invention.

FIGS. 5 and 6 respectively illustrate two embodiments of the waveguideused in the accelerator.

FIGS. 7 and 8 illustrate two variant embodiments of the accelerator inaccordance with the invention.

In all these figures, identical references indicate identical elements.

FIG. 1 shows a partial longitudinal section of a particle accelerator inaccordance with the invention. This accelerator comprises a vacuumenclosure 1 in which is located a particle source 2 (electron gun forexample), an accelerating structure 3 and means for injecting thehyperfrequency energy into said structure 3 which is constituted withelements e e e each comprising a cylindrical portion 5 provided with adiaphragm 6 which is in the form of a thin disc having a central opening7 for the passage of the beam. The assembly of these elements makes upthe cylindrical resonant cavities of the accelerating structure 3.

Each of these elements e e e comprises a certain number of notches 8 andfixing lugs 9, provided with a cylindrical hole, so that they can beassembled by means of rods 11. The neighbouring elements e e assembledon the rod 1] are then welded together along an annular surface 4.

The two ends of an accelerator section thus assembled, are respectivelyequipped with conventional input and output. The first element e, of theaccelerating structure 3 is coupled to a first junction or input coupler13. The input coupler 13 is designed to provide a matched junctionbetween a waveguide 14 and the cylindrical accelerator element e, and toexcite at the latter a TM-mode wave (preferably TM This waveguide 14 canbe a rectangular section waveguide as shown in FIG. 2 or anotherwaveguide as shown in FIG. 3 and 5 or FIG. 4 and 6. The FIG. 6illustrates an arcuate section waveguide and the FIG. 5 a vee-shapedwaveguide.

In FIG. 1, in order on the one hand to achieve a minimum bulk and on theother hand to group together the parts which carry high voltages (theelectron-gun 2 and the magnetron 24), the waveguide supplying UHF powerto an input coupler 13 is arranged parallel to the longitudinal axis ofthe structure 3.

The magnetron 24, here located close to the electron-gun 2, supplies inseries an isolator 25 and a flexible waveguide 26, arranged parallel tothe accelerating structure 3, and a flat elbow terminating in the sealedwindow 22 which is, in this case, located at the level of the exit ofthe accelerating structure.

Inside the enclosure 1, the UHF power has to be supplied to the inputcoupler 13 through a waveguide 14 of low height. The standard sectionwindow 22 is connected to the waveguide 14 of low height, through amatching section or coupler 20 whose dimensions reduce gradually.

The waveguide 14 is arranged, at the output of the acceleratingstructure 3, perpendicularly to the axis of said accelerating structure3 and is equipped with two openings 18 and 19 to pass the acceleratedelectrons towards the target.

A flat elbow 16 permits to the waveguide 14 to be parallel to theaccelerating structure and arranged between the cylindrical parts 5 ofthe elements e,.-..e,,, and the internal face of the enclosure 1. Thenotches 8 of the elements e ...e,, enable the waveguide 14 to pass alongit.

The waveguide 14 is connected to the input coupler 13 through an elbow15.

It should be pointed out that in order to gain space, it is possible toreplace a rectangular waveguide 14 as shown in FIG. 2 to a waveguidehaving a vee-shaped cross section 41 cross-section, (see FIG. 5) or anarcuate cross section 40 (see FIG. 6).

In this case, the elbows l5 and 16 which respectively connect thewaveguide 14, extending along the accelerating structure 3, with theinput coupler 13 and the other coupler 16 having rectangularcross-sections, have special shapes to match the UHF power channel.

The accelerating structure 3 illustrated in FIG. 1, has no externalmatched load to dissipate the residual UHF energy. This load is hereconstituted by a material 29 of a high resistivity alloy, covering theinternal surfaces of the elements (e,, e,, e,,) which are located at theexit extremity of the structure 3. This kind of material can be producedby means of an alloy of iron, chromium, cobalt and aluminium which isavailable commercially under the name of KANTHAL, or better an alloy ofnickel, chromium and aluminium which is commercially marketed under thename TOPHET H, for example. This latter alloy contains no ferromagneticelements (Fe) which is avantageous because the presence of the magneticfield generated, for example, by the coils used to focus the electronbeam and surrounding the accelerating structure (these coils have notbeen shown).

It should be pointed out that by reducing the number of cut-outs 8 andfixing lugs 9 in the elements e e,,, to three (instead of four), it ispossible to arrange into cut-outs 8 having substantially radial walls, awaveguide 14 of greater width, whose cut-off frequency is lower thanthat which it is possible to obtain with a waveguide of the kind shownin FIG. 2.

The embodiment illustrated in FIG. 7, comprises a matched load within awaveguide 30. An output coupler 42 is matched to the waveguide 30 and tothe last element e, of the accelerating structure 3. The waveguide 30will preferably have a cross-section identical to the section of thewaveguide 14 which supplies UHF power to the input coupler 13 (FIG. 1).The waveguide 30 is terminated in a matched load 31. This matched loadcan be replaced by the waveguide section which is internally coveredwith a resistive material and closed by a short-circuiting plate. Theresistive material used can be constituted by one of the aforementionedmaterials.

FIG. 8 illustrates another variant embodiment of the accelerator inaccordance with the invention.

In this embodiment, the input waveguide 32 is provided with three elbows33, 34 and 35 and is coupled on the one hand to the magnetron 24 and onthe other hand to the first element e, of the accelerating structure 3by means couplers 38 and 39.

A modulator assembly 50 supplies the cathodes of the magnetron 24 andthe particle source 2, (FIG. 1).

The accelerator in accordance with the present invention is a device ofreduced dimensions in order to make it easy to manipulate, and groupstogether the parts carried to very high voltages (cathodes), thusfacilitating the protection of the user. The modulator 30, theaccelerating structure 3, the magnetron 24 are including within a hood44.

Linear electron accelerators of this kind are intended primarily formedical application such as gamma radiography or radiotherapy, forexample.

What we claim is 1. A linear particle accelerator comprising a vacuumtight enclosure in which is located a source producing a particle beam,an accelerating structure, means for loading said accelerating structureand injecting means to inject hyperfrequency energy in said structure,said injecting means comprising at least a folded waveguide entirelylocated within said enclosure, along said accelerating structure saidstructure being formed with a succession of cylindrical elementsprovided with notches said waveguide being located within said notches.

2. A linear accelerator as claimed in claim 1, wherein said structure,having notches, carries at least a waveguide having a shape adaptedthereto.

3. A linear accelerator as claimed in claim 2, wherein said acceleratingstructure, having a cylindrical shape, is provided with notchescomprising substantially radial 1 walls, said waveguide having lateralplanar walls parallel to said radial walls and two other bent walls.

4. A linear accelerator as claimed in claim 3, wherein said bent wallsare arcuate.

5. A linear accelerator as claimed in claim 3, wherein said bent wallsare vee-shaped.

6. A linear accelerator as claimed in claim 1, further comprisinganother waveguide into said vacuum enclosure and extending along saidaccelerating structure, said waveguide being coupled thereto to the lastelement of said structure, said waveguide including said high-frequencyabsorbing substance.

7. A linear accelerator as claimed in claim 1, wherein the portion ofsaid waveguide extending in front of the end wall of said structure isprovided with two holes located along the beam path and facing oneanother.

1. A linear particle accelerator comprising a vacuum tight enclosure inwhich is located a source producing a particle beam, an acceleratingstructure, means for loading said accelerating structure and injectingmeans to inject hyperfrequency energy in said structure, said injectingmeans comprising at least a folded waveguide entirely located withinsaid enclosure, along said accelerating structure ; said structure beingformed with a succession of cylindrical elements provided with notches ,said waveguide being located within said notches.
 2. A linearaccelerator as claimed in claim 1, wherein said structure, havingnotches, carries at least a waveguide having a shape adapted thereto. 3.A linear accelerator as claimed in claim 2, wherein said acceleratingstructure, having a cylindrical shape, is provided with notchescomprising substantially radial walls, said waveguide having lateralplanar walls parallel to said radial walls and two other bent walls. 4.A linear accelerator as claimed in claim 3, wherein said bent walls arearcuate.
 5. A linear accelerator as claimed in claim 3, wherein saidbent walls are vee-shaped.
 6. A linear accelerator as claimed in claim1, further comprising another waveguide into said vacuum enclosure andextending along said accelerating structure, said waveguide beingcoupled thereto to the last element of said structure, said waveguideincluding said high-frequency absorbing substance.
 7. A linearaccelerator as claimed in claim 1, wherein the portion of said waveguideextending in front of the end wall of said structure is pRovided withtwo holes located along the beam path and facing one another.